OPTIMIZING THE C-13-N-14 REAPDOR NMR EXPERIMENT - A THEORETICAL AND EXPERIMENTAL-STUDY

The optimum N-14 pulse lengths in the C-13-N-14 rotational-echo adiaba tic-passage double-resonance (REAPDOR) NMR experiment are determined f rom calculations and from experiments on samples of glycine and L-alan ine. The REAPDOR experiment utilizes the adiabatic passages that N-14 spins make between the N-14 Zeeman energy levels during the applicatio n of a single, short N-14 radiofrequency pulse. Use of a short N-14 ir radiation time of less than one-quarter of a rotor period ensures that the number of N-14 spins that undergo more than one passage is minimi zed. This simplifies calculations describing C-13 dipolar dephasing an d provides better agreement between calculations and experiments. Reco very of the C-13-N-14 dipolar couplings and N-14 quadrupolar coupling constants and asymmetry parameters is described. (C) 1998 Academic Pre ss.